Introduction

Trichogramma chilonis(Ishii) is a small, tiny wasp that belongs to the family Trichogrammatidae, which consists of various egg parasitoids that target insect eggs. These wasps primarily parasitize eggs of moths and butterflies, certain species within the genus also parasitize eggs of beetles, lacewings and their relatives1,2. Trichogramma wasps are naturally found in diverse terrestrial and some aquatic habitats. They play a crucial role in combatting significant lepidopteran pests that affect field crops, forests, fruit trees and vegetables. However, in many crop production systems, the existing populations of Trichogrammaalone are insufficient to effectively control and prevent these pests from causing substantial damage3. Due to its potential as biological control agents, entomologists began large-scale production of Trichogramma in the early 1900s. The purpose was to rear these wasps in large quantities for insect pest control. Presently, Trichogrammaspecies are extensively employed worldwide as natural enemies against insects due to their ease of mass production and their ability to target numerous economically important crop insect pests4. These wasps can eliminate host eggs through a feeding process. They sting the host egg and consume the liquid droplet that appears at the sting site, without depositing their own eggs. This feeding behavior plays a significant role in pest control. Additionally, the tiny Trichogramma adults obtain nourishment from water and sweet substances present in the field. These wasps spent most of their time finding proper host eggs. When a female Trichogrammalocates host eggs, she penetrates the eggshell, known as the chorion, by creating a hole. Depending on the size of the host egg, she deposits one or more of her own eggs inside5. The parasitoid larva hatches from the deposited egg and continues to consume the contents of the host egg, ultimately leading to the death of the host. The larva undergoes three distinct developmental stages before pupating within the host egg. This parasitic process causes the parasitized host eggs to darken and appear black6,7. T. chilonis has been widely recognized for its high efficacy in parasitizing the eggs of Helicoverpa armigera, significantly reducing pest populations in various crops while exhibiting specificity and minimal ecological disruption1. The American bollworm (Helicoverpa armigera) is a major agricultural pest, causing significant economic damage to a wide range of crops globally, including cotton, legumes, and vegetables. In cotton, it is responsible for yield losses ranging from 30 to 80%, contributing to annual economic losses exceeding $1 billion in India alone8. Globally, the damage caused by H. armigera across various crops exceeds $5 billion annually, with severe impacts on tomatoes (up to 50% yield loss), chickpeas (20–30% loss, valued at $328 million annually), and maize and sorghum (up to 30% yield reduction)9. The use of synthetic insecticides is a widely employed method for managing H. armigerapopulations globally10. These chemical insecticides are recognized as highly effective in safeguarding crops from pests at various stages, offering immediate control over the entire pest population11,12. However, despite their benefits, the use of synthetic insecticides poses environmental concerns13,14. The intricate chemical composition of pesticides, their persistence in the environment, and their toxic effects on animals, humans, as well as the risks of bioaccumulation, contribute to the critical issue of chemical pollution15.

Several studies have evaluated the effects of insecticides on Trichogrammaspp., revealing varying levels of toxicity16,17. For instance, Spinosad, thiamethoxam, and oxamyl were tested on T. pretiosum, with toxicity ranked as thiamethoxam > Spinosad > oxamyl18. Another study reported that Emamectin benzoate, lufenuron, and imidacloprid significantly reduced the emergence of T. chilonis when exposed during immature stages inside Sitotroga cerealella eggs, showing survival rates of 70.02%, 27.62%, and 18.48%, respectively, after 3 h. However, after 24 h, none of these insecticides were safe for adult T. chilonis19. Another study reported that lufenuron showed the least negative impact on parasitism and viability of T. pretiosumpopulations20. Overall, laboratory and field studies indicate that Trichogramma wasps are highly susceptible to most broad-spectrum insecticides, often undermining the success of biological control programs due to the detrimental effects of these chemicals on beneficial insects.

The adverse impacts of chemical insecticides on natural biological control agents emphasize the necessity for research and the development of pest control strategies that go beyond reliance on pesticides, including the implementation of bio-control practices21. Currently, crop protection policies emphasize the reduction of non-selective pesticide usage to safeguard crops against insects. Consequently, it is crucial to thoroughly investigate the potential adverse effects of these pesticides, particularly on natural enemies, and eliminate the use of insecticides that pose harm to them22. The integration of chemical and biological control organisms is often crucial for the success of integrated pest management programs, particularly when dealing with complex pest populations23. Despite the significant contribution of biological control agents in agriculture, chemical control remains essential. However, the extensive use of nonselective insecticides significantly diminishes the beneficial impact of biocontrol agents, especially parasitic Hymenoptera, which are often more vulnerable to insecticides compared to their hosts. In addition to direct toxicity, insecticides can disrupt the feeding behavior of biocontrol agents by acting as repellents, inhibitors, or disruptors of olfaction.

The neonicotinoid insecticide, Imidacloprid, is extensively used to control a broad range of sucking insect pests, including aphids, whiteflies, tobacco budworm and leafhoppers, in various crops. Imidacloprid acts as an agonist of insect nicotinic acetylcholine receptors (nAChRs), disrupting neural transmission and leading to paralysis and death24. It is known for its systemic properties, providing long-lasting protection when applied as a seed treatment, soil drench, or foliar spray. Due to its high efficacy and ease of application, Imidacloprid has become one of the most widely used insecticides worldwide and is an integral component of pest management programs in crops like cotton, tomato, and citrus25,26. The ivermectin derivative, Emamectin Benzoate, is a highly effective insecticide widely used for controlling lepidopteran pests in various crops. Emamectin Benzoate primarily targets insect γ-aminobutyric acid (GABA)-gated chloride channels, leading to paralysis and mortality27. Known for its high potency and low mammalian toxicity, it is particularly effective against pests like Helicoverpa armigera and Spodopteraspecies. The use of Emamectin Benzoate has gained significant popularity among growers in many countries, including Pakistan, due to its broad-spectrum activity and compatibility with integrated pest management (IPM) strategies28,29. The pyrethroid insecticide, Bifenthrin, is widely utilized for managing a broad spectrum of insect pests, including lepidopterans, aphids, and whiteflies, across various crops. Bifenthrin acts by modulating sodium channel function in the insect nervous system, leading to prolonged nerve excitation, paralysis, and eventual death30. It is valued for its high contact and residual activity, making it effective in both agricultural and structural pest control. Its broad-spectrum efficacy and relatively low environmental persistence have contributed to its popularity among growers, particularly for crops such as cotton, maize, and vegetables31,32. The anthranilic diamide insecticide, Chlorantraniliprole, is highly effective against a wide range of lepidopteran pests in crops such as maize, rice, and vegetables. It acts by selectively activating ryanodine receptors in insect muscle cells, causing uncontrolled calcium release, muscle paralysis, and death33. Renowned for its novel mode of action, Chlorantraniliprole exhibits high potency at low application rates and is considered environmentally friendly due to its low toxicity to non-target organisms, including pollinators and natural enemies34. Its systemic and translaminar properties make it a preferred choice in integrated pest management (IPM) programs worldwide35. The benzoylurea insecticide, Novaluron, is an insect growth regulator (IGR) widely used to control immature stages of various insect pests, including lepidopterans, coleopterans, and dipterans, in crops such as cotton, vegetables, and citrus. Novaluron disrupts chitin synthesis during molting, preventing normal development and leading to mortality in target pests36. It is highly effective against juvenile stages and has minimal impact on non-target organisms, including pollinators and natural enemies, making it an important component of integrated pest management (IPM) strategies. Novaluron’s selective activity and environmental safety profile have contributed to its widespread adoption in sustainable agriculture37,38.

Synthetic insecticides play a pivotal role in managing H. armigera, yet their non-target impacts on essential biological control agents like T. chilonisare not well-documented, particularly in tomato-growing regions of Pakistan. Previous studies often lack a comprehensive evaluation of these effects under controlled laboratory conditions, which is vital for optimizing integrated pest management (IPM) strategies13,39.Therefore, this study aims to fill this gap by assessing the impact of five widely used insecticides on T. chilonis, providing critical insights into sustainable pest management.

Materials and methods

Host rearing (Sitotroga Cerealella)

S. cerealella eggs were introduced into trays measuring 30 × 25 × 4 cm3. These trays consisted of two main components: the upper rectangular part (37 × 37 × 5 cm3) constructed from tin sheets, which served as the mass rearing chamber and the lower part that tapered downwards with an opening size of 3 × 3 cm2 where the adults were collected. The mass rearing chamber contained approximately 5 kg of sterilized wheat grains, which served as the food source for S. cerealella larvae and adults. The trays were covered with mesh cloth for ventilation and maintained at 28 ± 2°C, 65 ± 5% RH in darkness at incubator. In the upper section of the mass rearing chamber, the hatching larvae were provided with wheat grains for nourishment. Subsequently, they pupated and within 3–4 weeks, the adult moths emerged. These adult moths were directly collected in the attached adult collecting box. The adult collecting boxes were replaced daily with new ones to ensure efficient collection. The collected adult moths were then transferred to plastic rearing jars having lid at the top and a 75-mesh size sieve at the bottom and were placed in a plate containing starch for eggs laying. The adults laid eggs, which were subsequently gathered by sifting the starch through mesh sizes number 70 and 50. The eggs were collected and incubated for further experiments as per the methodology of Saljoqi et al.40.

Trichogramma chilonis rearing on host eggs

For this purpose, around 10 mated pairs of S. cerealella adults were transferred into a plastic jar having a lid at the top and a 75-mesh size sieve at the bottom and were placed in a plate containing starch for eggs laying. After 24 h, S. cerealella eggs were collected and observed under a binocular microscope. Around 200 uniform size eggs were separated and then evenly distributed on a gummy paper card measuring 4 × 4 cm². This was achieved by employing a common 50 ml plastic bottle with a lid, equipped with a mesh size of 30–45, which facilitated the sprinkling process. The prepared Trichocards were then allowed to dry for a period of 1 to 2 h at room temperature. The dried Trichocards were subsequently placed in glass jars measuring 5 × 12 cm² in incubator set at 25 ± 30 °C, 65 ± 5% RH and 16:8 h (L: D) photoperiod. These jars contained approximately 40–50 T. chilonis adults of both genders and were left for at least 24 h to allow for parasitism. To optimize parasitism, the glass jars were placed under a tube light. Each jar was securely sealed with nylon cloth to prevent T. chilonis adults from escaping. After the parasitism phase, the Trichocards containing parasitized hosts were transferred to new, empty rearing jars of identical dimensions. These jars were subsequently placed in an incubator set to maintain controlled conditions, maintaining a temperature range of 25–30ºC and a relative humidity of 60–70%.This allowed the parasitoids to emerge from the host eggs. On a daily basis, numerous parasitized Trichocards were collected using the same method and incubated in the same environmental conditions. This process ensured the maintenance of the Trichogramma culture for future experimental purposes.

Insecticides

Five insecticides i.e. Emamectin Benzoate (Proclaim®, 19% EC, Syngenta Co., Pakistan), Imidacloprid (Imidacloprid®, 70% WS, FMC, Pakistan), Novaluron (Uniron®, 10% EC, ICI LTD., Karachi, Pakistan) Chlorantraniliprole (Coragen®, 20% SC, FMC, Pakistan) and Bifenthrin (Talstar® ,10% EC, FMC, Pakistan) were purchased from local market Peshawar.

Bioassays

The experiment was carried out in the Biological Control Laboratory of Sugar Crop Research Institute (SCRI) Mardan. T. chilonis adults were collected from the parasitized eggs of S. cerealella from sugarcane crop in Mardan, Khyber Pakhtunkhwa Province, Pakistan. In the experiments, the recommended field concentrations of various insecticides were evaluated. The chemical solutions were prepared by mixing distilled water in accordance with their recommended doses. To evaluate the toxicity of the different insecticides on pupal stages of T. chilonis, ten cards each having 20 eggs of S. cerealella were glued into paper cards. These cards were then sprayed with each insecticide of given dose following procedure of Badshah et al.41. Each eggs card was sprayed with 1 mL of insecticide per treatment, ensuring uniformity by maintaining consistent sprayer pressure, nozzle distance, and spray angle across all applications. The egg cards were then shade dried for 10 to 15 min. Thereafter, the cards were placed in a vial and were exposed to newly emerge (6) females for 24 h hours in glass jars measuring 5 × 12 cm² in incubator set at 25 ± 30 °C, 65 ± 5% RH and 16:8 h (L: D) photoperiod. After 24 h, the females were removed from these vials. A sufficient number of adult parasitoids were utilized to ensure nearly 100% parasitization of the host eggs provided. These parasitoid cards were maintained under control conditions in the incubator. The experiments were carried out using a completely randomized design (CRD) with 10 replications. Data was collected for the following parameters.

Life table parameters of Trichogramma chilonis

The life table parameters of T. chilonis, as affected by different insecticides, were studied using the methodology described by Bayram et al.42 with some modifications. To study the life table parameters of T. chilonis, ten cards, each having 20 eggs of S. cerealella, were glued into paper cards. These cards were then sprayed with each insecticide of given dose following procedure of Badshah et al. (2016). The life stages of the T. chilonis were grouped into two stages i.e. from eggs to pupae as preadult stage and adult stage as male and female and were closely monitored. The data were collected at regular intervals to accurately assess the duration of each life stage and the relevant parameters such as fecundity, longevity, pre-oviposition period and total oviposition period. Newly emerged adult T. chilonis individuals (> 4 h after emergence) from treated cards were introduced into 15 ml flasks containing a food source consisting of honey products. To prevent the escape of adults and facilitate air circulation, the flasks were covered with nylon cloth and were placed in the incubator maintaining a temperature range of 25–30ºC and a relative humidity of 60–70%. Fecundity and longevity of T. chilonis were determined following the procedure outlined by Bayram et al.42. Each vial containing a female adult parasitoid was provided with an egg card containing 200 S. cerealella eggs. The egg cards were replaced with new ones after 24 h, and this process was repeated daily until the death of all T. chilonis individuals. The survival of female parasitoids was recorded daily to determine their longevity. The labeled egg cards were placed in glass tubes (5.5 cm and 1 cm in diameter) and incubated under standard laboratory conditions for 13 days to allow the complete emergence of offspring from the initially parasitized eggs. The number of parasitized eggs (indicated by a black color) was calculated for each treatment.

Sex ratio

The sex ratio was determined by observing the adults that emerged during the experiment under a stereomicroscope at 10X magnification. An identification key and morphological characteristic were employed to differentiate between male and female individuals43. The adults were made immobilized by placing them in cold surface for 1–2 min in petri dishes. After immobilization, the adults were placed under a stereomicroscope for proper identification based on characters as mentioned below.

Male parasitoid Male individuals can be distinguished from females based on several morphological characteristics. Males are generally smaller in size and have a darker coloration. They exhibit short and round abdomen with a distinct black color. Their antennae are long and prominently featured, adorned with long bristles. The dorsum of the thorax is typically brown in color with a hint of black.

Female parasitoid Females are typically larger than males and have a pale coloration. Their antennae are short and have small bristles. The body color of females is yellowish-orange, and they have a distinct and sharp abdomen.

Percent parasitism of T. Chilonis

To determine the percent parasitism of Trichogramma chilonis on Sitotroga cerealella eggs, 200 freshly laid eggs were taken from established cultures. These eggs were evenly distributed on sticky cards measuring 3 × 2 cm. Each treatment involved 10 cards, with 20 eggs on each card. The egg cards were sprayed with the recommended dose of the respective chemical treatment and allowed to dry. Subsequently, the treated cards were individually placed in glass jars containing freshly mated adult females of T. chilonisfor a 24-hour parasitization period. The exposed eggs were then stored in separate glass jars under controlled laboratory conditions (25 ± 2 °C, 65 ± 5% relative humidity, and an 8:16 light-to-dark cycle) until the parasitized eggs turned black, signifying parasitoid development. The blackened egg cards were collected and examined for parasitism. The percent parasitism was calculated using a standard formula44.

$$\:\text{P}\text{e}\text{r}\text{c}\text{e}\text{n}\text{t}\:\text{p}\text{a}\text{r}\text{a}\text{s}\text{i}\text{t}\text{i}\text{s}\text{m}\:=\frac{\text{N}\text{o}.\;\text{o}\text{f}\:\text{p}\text{a}\text{r}\text{a}\text{s}\text{i}\text{t}\text{i}\text{z}\text{e}\text{d}\:\text{e}\text{g}\text{g}\text{s}\:\text{i}\text{n}\:\text{t}\text{r}\text{e}\text{a}\text{t}\text{m}\text{e}\text{n}\text{t}}{\text{T}\text{o}\text{t}\text{a}\text{l}\:\text{N}\text{o}.\:\text{o}\text{f}\:\text{e}\text{g}\text{g}\text{s}\:\text{o}\text{f}\text{f}\text{e}\text{r}\text{e}\text{d}}\times\:100$$

Statistical analysis

The survival rate (sxj) for each age-stage of T. chilonis was calculated using the formula:

$$\:{s}_{xj}=\frac{{n}_{xj}}{{n}_{01}}$$

where “n01” represents the initial number of eggs at the start of the study, and “nxj” denotes the number of individuals surviving to age x and stage j. The age-specific survival rate (lx) was determined using the summation, \(\:{l}_{x}={\sum}_{j=1}^{m}{s}_{xj}\). Where the summation spans all stages (j). Female age-specific fecundity (fx4) was computed as:

\(\:{f}_{x4}=\frac{{E}_{x}}{{n}_{x4}}\).where Ex is the total number of eggs laid by all females at age x, and nx4 is the number of females at the same age.

The net reproductive rate (R0)—the average number of offspring a female produces over her lifetime—was calculated as: \(\:{R}_{0}={\sum}_{x=0}^{\infty}{\sum}_{j=1}^{m}{s}_{xj}{f}_{xj}\), where m represents the number of life stages. The intrinsic rate of increase (r) was determined using the Lotka-Euler equation:

$$\:\mathop{\sum}\limits_{x=0}^{\infty\:}{e}^{-r\left(x+1\right)}{l}_{x}{m}_{x}=1$$

The gross reproductive rate (GRR) was estimated as: \(\:GRR={\sum}{m}_{x}\)

The finite rate of increase (λ) was calculated as: as \(\:\lambda\:={e}^{r}\).

The age-specific life expectancy (ex), which indicates the expected lifespan for individuals of age x, was also computed as: \(\:{e}_{x}=\frac{\sum_{i=x}^{n}{l}_{i}}{{l}_{x}}\)

Using the age-stage two-sex life table theory, the reproductive value (vx) for T. chilonis was determined based on its contribution to future generations and was calculated as: \(\:{v}_{x}=\frac{{e}^{-r(x+1)}}{{l}_{x}}{\sum}_{i=x}^{\infty\:}{e}^{-r(i+1)}{l}_{i}{m}_{i}\)

Since T. chilonis populations were group-reared, individual-reared data were derived for accurate analysis of life table parameters. To evaluate differences among treatments, the paired bootstrap method with 100,000 resamples was employed45 (Efron, & Tibshirani 1993). The analysis of survival rate (sxj), age-specific survival rate (lx), fecundity (mx), net reproductive rate (R0), intrinsic rate of increase (r), gross reproductive rate (GRR), finite rate of increase (λ), life expectancy (ex), and reproductive value (vx) was performed using the TWOSEX-MSChart software46,47,48,49,50,51,52. No significant mortality was observed in the control groups unrelated to the treatments. Strict protocols were followed to minimize external factors, including maintaining a sterile environment, using uncontaminated materials, and providing optimal rearing conditions. Any natural mortality in the control group was recorded and considered during data analysis to ensure accurate interpretation of results. The data regarding the percent parasitism of T. chilonis was analyzed by one way analysis of variance and the means were compared using LSD test at 5% level of significance using Statistix software version 8.1.

Results

The results regarding the effect of different insecticides on the life table parameters of T. chilonis are presented below.

Effect of different insecticides on different developmental parameters of T. Chilonis under laboratory conditions

The effect of different insecticides on the preadult and adult developmental parameters of T. chilonis is summarized in Table 1. The results reveal that different insecticides significantly affected the preadult survival rate, mortality rate of preadult stage, total preoviposition and oviposition period, fecundity, female total longevity, male total longevity, and total longevity compared to the control. The result shows that no significant differences were observed in the mean preadult stage duration (days) following application of different insecticides (F = 44.775, DFs = 5, 915). The results further show that the different insecticides had significantly affected the preadult survival and mortality rate of T. chilonis (F = 1823.12, DFs = 5,1194). The host eggs treated with Imidacloprid resulted in significantly lower preadult survival rate (P = 0.0000, 0.635%) and higher mortality rate (0.365%), followed by host eggs treated with Chlorantraniliprole, while significantly higher survival and lower mortality rate were observed in the control. The host eggs treated with Imidacloprid prolong the total pre-oviposition period of the T. chilonis (8.82 ± 4.79 days) compared to other treatments while lowest values of TPOP were recorded in Bifenthrin, Novaluron and control (8.77 ± 4.64, 8.78 ± 0.35 and 8.76 ± 4.28 days). The results further show that the different insecticides had caused significant effect on the oviposition period of T. chilonis (F = 492.63, DFs = 5,478). A significantly higher oviposition period of the emerged adult females was observed in the control (5.80 ± 0.075 days), this was followed by adult females emerge from the host eggs treated with Bifenthrin and Emamectin Benzoate with 5.60 ± 0.086 and 5.54 ± 0.100 days respectively. The adults emerge from the treated host eggs with Imidacloprid and Chlorantraniliprole insecticides resulted in significantly lower oviposition days (5.25 ± 0.108 and 5.18 ± 0.112) days respectively. The results regarding the female total longevity show that the different insecticides had significantly affected the total longevity of the female adult as compared to control (P ≤ 0.000, F = 405.52, DFs = 5,525). The female adult longevity of the T. chilonis was recorded significantly lower in Chlorantraniliprole and Imidacloprid (14.07 ± 0.11 and 14.13 ± 0.10) days respectively, while significantly higher female adults longevity was recorded at Bifenthrin and control i.e. (14.43 ± 8.68 and 14.60 ± 7.49)days respectively. The results regarding the male total longevity showed no significant difference for the different treatments (F = 1.738, DFs = 5, 384). The results regarding the total longevity of the T. chilonis adults showed significant differences among the different treatments (F = 2303.73, DFs = 5,1194). Significantly lower total longevity (12.41 ± 0.13 days) was recorded in eggs treated with Imidacloprid and maximum in control (13.65 ± 0.11 days). The results regarding the mean fecundity of T. chilonis show that the insecticide Imidacloprid was found significantly toxic resulting in significantly minimum mean number of eggs (P = 0.000, F = 890.51, DFs = 5, 525, 69.75 ± 3.39 eggs) as compared to other treatments while the insecticide Bifenthrin and Novaluron was found least toxic with mean fecundity of (89.98 ± 2.64 and 86.51 ± 3.07 eggs) respectively. The significantly higher mean fecundity of T. chilonis was recorded in control (96.90 ± 2.43 eggs).

Table 1 Effect of different insecticides on different developmental parameters of T. Chilonis under laboratory conditions.
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Effect of different insecticides on life table parameters of Trichogramma chilonis

The lethal toxicity effect of different insecticides against life parameters of T. chilonis are presented in Table 2. The bootstrap results reveal that different insecticides significantly affected the life table parameters of T. chilonis including r, λ, R0, T and DT. The results regarding the intrinsic rate of increase (r) show significant differences among the different treatments (P = 0.0000, F = 1441.36, DFs = 5,1194). Significantly lowest value of (r) was recorded following imidacloprid application (0.28 ± 9.62), this was followed by host eggs treated with Chlorantraniliprole and Emamectin Benzoate. The significantly higher values of r were recorded at host eggs treated with Novaluron, Bifenthrin and control with 39.36 ± 3.34, 0.32 ± 7.42 and 0.34 ± 6.70 respectively. The finite rate of increase (λ) of the T. chilonis was also significantly affected following different insecticides application (P = 0.000, F = 1446.06, DFs = 5,1194). The significantly higher value for the finite rate of increase (λ) was recorded in control, Bifenthrin and Novaluron i.e. 1.41 ± 9.45, 1.39 ± 1.03 and 1.38 ± 1.09 respectively. The results regarding the net reproductive rate (R0) also show significant differences among the various treatments (P = 0.000, F = 1559.93, DFs = 5, 1194). A significantly lower value of (R0) was recorded for Imidacloprid (25.11 ± 2.65 eggs per individual) followed by Chlorantraniliprole and Emamectin Benzoate with 31.29 ± 2.98 and 35.51 ± 3.20 eggs per individual) respectively. The insecticide Bifenthrin and Novaluron were found relatively safe with significantly higher value of (R0) i.e. 42.74 ± 3.40 and 39.36 ± 3.34 eggs per individual) respectively. The data regarding the mean generation time (T) of T. chilonis following insecticides application shows non-significant difference (P ≥ 0.05, F = 83.941, DFs = 5, 1194). A lower value of the mean generation time (T) was recorded for Novaluron (11.32 ± 6.22 days) while maximum generation time was recorded in eggs treated with Imidacloprid (11.43 ± 5.68 days). The results regarding the gross reproductive rate (GRR) also show significant differences among the various treatments (P = 0.000, F = 770.78, DFs = 5, 1194). A significantly lower gross reproductive rate (49.38 ± 4.53) offsprings were produced in host eggs treated with Imidacloprid. This was followed by Chlorantraniliprole and Emamectin Benzoate with 53.87 ± 4.56 and 59.13 ± 4.00 offsprings respectively. Finally, the data regarding the mean doubling time (DT) of T. chilonis was also found significantly different among the various treatments (P = 0.000, F = 1372.04, DFs = 5, 1194). The value of (DT) was recorded significantly maximum in eggs treated with Imidacloprid (2.45 ± 8.53), followed by Chlorantraniliprole and Emamectin Benzoate (2.29 ± 6.73 and 2.21 ± 5.96), while significantly lowest value of (DT) was recorded in Novaluron, Bifenthrin and in eggs treated with control condition i.e. (2.13 ± 5.28, 2.10 ± 4.78, 2.01 ± 3.95 days) respectively.

Table 2 Effect of different insecticides on life table parameters of Trichogramma chilonis under laboratory condition.
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Survival rate (s xj) of T. Chilonis

The survival rate of T. chilonis under laboratory conditions when exposed to different insecticides is illustrated in Fig. 1a-f. Due to the different developmental time of T. chilonis, significant overlapping was observed among the curves of the different treatments. The total developmental time of T. chilonis from egg to adult stage in all the treatments was recorded 16 days. Maximum survival rate of the male and female adults of T. chilonis were 0.135 and 0.135% on day 8 in control, this was followed by Bifenthrin and Novaluron treated female and male survival rate with 0.115 and 0.120% and 0.15 and 0.15% on day 8 respectively. The survival rate of adults of T. chilonis female and male when treated with Emamectin Benzoate were 0.435 and 0.325% respectively on day 9. Similarly, the survival rate of adults of T. chilonis female and male when treated with Chlorantraniliprole were 0.405 and 0.305% respectively on day 9. While lowest survival rate of adults of T. chilonis female and male (0.360 and 0.275%) were recorded on day 9 when treated with Imidacloprid respectively.

Fig. 1
figure 1figure 1

a-f Effect of different insecticides on survival rate (sxj) of T. chilonis under laboratory conditions.

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Effect of different insecticides on the age-specific survival rate (l x), of Trichogramma chilonis

Figure 2a-f shows the effect of different insecticides on the age-specific survival rate (lx), age-stage fecundity of the female stage (fx) age-specific fecundity (mx), and age-specific maternity (lxmx) of T. chilonis under laboratory conditions. The curves regarding the age specific survival-rate (lx) of T. chilonis in Fig. 2a-f show that the (lx) curve of T. chilonis treated with Imidacloprid and Chlorantraniliprole drop more quickly as compared to the other treatments. The curves regarding age-stage specific fecundity (fx) show that maximum fecundity of T. chilonis were recorded in control (20.32 offspring per day) on day 10, followed by Bifenthrin with 19.26 offspring per day on day 10 and Novaluron with 19.43 offspring per day on day 10. Eggs treated with Chlorantraniliprole resulted in 17.82 offspring per day on day 10 followed by Emamectin Benzoate with 17.80 offspring per day and Imidacloprid with 15.54 offspring per day. The age specific fecundity (mx) curve illustrates that T. chilonis adults started eggs laying on day 8 and reaches to maximum on day 10 (11.98 eggs per day) in control, this was followed by Bifenthrin (11.15eggs per day) and Novaluron (11.19 eggs per day). The other treatments resulted in significantly lower value of age specific fecundity (mx) of T. chilonis. The curves regarding the age-specific maternity (lxmx) of T. chilonis show that greatest value of lxmx (10.66 offspring) was observed on control condition on day 10 followed by Bifenthrin (9.15 offspring) and Novaluron (8.84 offspring) respectively. The age-specific maternity (lxmx) of T. chilonis in eggs treated with Emamectin Benzoate, Chlorantraniliprole and Imidacloprid resulted in significantly lower value (7.74, 7.22, 5.59 offspring) on day 10 respectively (Fig. 2a-f).

Fig. 2
figure 2figure 2

a-f Effect of different insecticides on the age-specific survival rate (lx), age-stage fecundity of the female stage (fx) age-specific fecundity (mx), and age-specific maternity (lxmx) of Trichogramma chilonis under laboratory conditions.

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Age-stage specific life expectancy (e xj) of Trichogramma chilonis

Figure 3a-f illustrates the effect of various insecticides on age specific life-expectancy (exj) of T. chilonis. The different curves in Fig. 3a-f show that the life expectancy (exj) of pre-adult, male and female T. chilonis adults were recorded maximum at the time of emergence (13.65,5.39 and 6.60 days) in control condition followed by Bifenthrin with (13.27, 5.39 and 6.43 days) and Novaluron with (13.04, 5.40 and 6.19 days) respectively. The effect of Emamectin Benzoate and Chlorantraniliprole on life expectancy (exj) of the pre adult, male and female T. chilonis adults were (13.00, 5.39 and 6.37 days) and (12.67, 5.37 and 6.07 days) respectively. Imidacloprid resulted in lower exj values of (12.41, 5.36 and 6.13 days) respectively at the time of emergence of pre-adult, male and female T. chilonis adults.

Fig. 3
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a-f Age-stage specific life expectancy (exj) of Trichogramma chilonis under laboratory conditions.

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Age-stage specific reproductive rate (v xj) of Trichogramma chilonis

The effect of different insecticides on T. chilonis reproductive value (vxj) is illustrated in Fig. 4a-f. The vxj of preadult of T. chilonis was recorded high (20.01 offspring per day) on day 8 in control, this was followed by Bifenthrin (17.34 offspring per day) on day 8 and Novaluron (16.06 offspring per day) on day 8. The age stage specific reproductive values (vxj) of pre-adult of T. chilonis were (13.47 offspring per day) in Chlorantraniliprole on day 8 followed by Emamectin Benzoate (14.91 offspring per day) on day 8 and lowest value of (vxj) of T. chilonis (11.11 offspring per day) on day 8 when treated with Imidacloprid. The (vxj) curve for the female reproductive showed the highest reproductive value (vxj) of (55.75 offspring) in control condition followed by Novaluron (53.33 offspring) and Bifenthrin (53.19 offspring) on day 08 respectively. Emamectin Benzoate showed the highest female reproductive value (vxj) of (49.89 offspring), this was followed by Chlorantraniliprole (47.86 offspring) and Imidacloprid (44.19 offspring) on day 08 respectively.

Fig. 4
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a-f Age-stage specific reproductive rate (vxj) of Trichogramma chilonis under laboratory conditions.

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Effect on different insecticides on percent parasitism and sex ratio of T. Chilonis

Table 3 shows the effect on different insecticides on percent parasitism and sex ratio of T. chilonis under laboratory condition. The data show that different insecticides significantly affected the % parasitism and sex ratio of T. chilonis. The results show that maximum percent parasitism was noted in control, Bifenthrin and Novaluron. The insecticides Imidacloprid and Chlorantraniliprole were found to be more toxic and resulted in minimum % parasitism (63.5% and 71%) respectively. The data regarding the male and female number show that maximum mean number of females had emerged in control, followed by Bifenthrin and Novaluron, while minimum in Chlorantraniliprole and Imidacloprid, the insecticides Emamectin Benzoate was found slightly toxic with mean no of males (65) and females (87).

Table 3 Effect of different insecticides on percent parasitism and sex ratio of T. Chilonis under laboratory condition.
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Discussion

Chemical pesticides are widely used to manage agricultural pests around the world. However, they often exert lethal and sublethal effects on the bio-control agents that target these pests53. T. chilonis, a common egg parasitoid of Helicoverpaspecies in tomato growing areas of Pakistan, faces detrimental impacts on its key functions such as foraging, parasitism and mate searching due to the use of these insecticides54. The judicious and selective use of insecticides represents a suitable strategy in pest management, aiding in the conservation of natural enemies of the pests within the agro ecosystem. Our results revealed that all the tested synthetic insecticides negatively affected T. chilonis performance at recommended doses, although some of them were found safe for use against T. chilonis. Imidacloprid and Chlorantraniliprole significantly reduced the mean fecundity of T. chilonis and resulted in reduced mean fecundity data and adult emergence rate as compared to Bifenthrin and Novaluron. Additionally, host eggs treated with Imidacloprid and Chlorantraniliprole significantly prolonged the total pre-oviposition period of the T. chilonis (8.82 ± 4. 79 and 8.81 ± 4.54 days) compared to other treatments. Similar results were also published by Saber (2011), who tested Imidacloprid and fenofenth against T. chilonis and reported that Imidacloprid posed 109 times more risk and Hazard Quotient to T. chilonis. Candolfi et al.55 and Campbell et al.56 also observed higher Hazard Quotient for Imidacloprid against T. chilonis. Similarly, Suh et al.57 reported that the penetration of insecticides into host eggs varies by type, affecting parasite emergence rate. They further observed that some insecticides have minimal penetration, resulting in less impact on wasp emergence, while residues on egg chorions can harm emerged adults. Garcia et al.58 also reported that pyrethroids exhibit high residual toxicity, inhibiting adult wasp emergence. Our results further confirm that all selected insecticides significantly affected the values of R0, r, λ, T and DT. Life table parameters such as the net reproductive rate (R₀), intrinsic rate of increase (r), finite rate of increase (λ), mean generation time (T), and doubling time (DT) are essential for understanding the population dynamics of Trichogramma chilonis under the influence of synthetic insecticides. These parameters provide insights into how insecticides may impact the parasitoid’s efficacy as a biological control agent. The net reproductive rate (R₀) represents the average number of offspring that an individual can produce over its lifetime in a specific environment. Similarly, the intrinsic rate of increase (r) reflects the per capita growth rate of a population, serving as a key indicator of its capacity to recover and expand59. A high r allows T. chilonis populations to rapidly increase and outpace pest populations. However, synthetic insecticides can reduce r, slowing population recovery and diminishing the biological control potential60. The current study demonstrated significant differences in the net reproductive rate (R₀) and intrinsic rate of increase (r) of T. chilonis exposed to different insecticides. The significantly higher R₀ values observed with Bifenthrin and Novaluron treatments (50.87 ± 3.65 and 42.74 ± 3.40 eggs per individual and 0.32 ± 7.42 and 0.32 ± 7.93 offspring per day respectively) suggested that these insecticides exert minimal negative effects on the reproductive potential of T. chilonis. This can be attributed to their lower toxicity or sublethal impact on the parasitoid’s reproductive biology. Bifenthrin, a pyrethroid, is known for its selective activity against target pests while exhibiting relatively low toxicity to non-target beneficial insects when used at appropriate concentrations13. Similarly, Novaluron, an insect growth regulator (IGR) that inhibits chitin synthesis, primarily affects the immature stages of insects and has limited direct toxicity to adult parasitoids61 These attributes likely allowed T. chilonis to maintain higher reproductive rates in the presence of these insecticides. In contrast, Imidacloprid and Chlorantraniliprole treatments resulted in significantly lower R₀ and r values. Imidacloprid, a neonicotinoid, acts on the nervous system by binding to nicotinic acetylcholine receptors, which may disrupt the physiological processes of T. chilonis, including reproduction62. Chlorantraniliprole, a diamide insecticide, targets ryanodine receptors and disrupts calcium homeostasis in insects. Although primarily designed to control chewing pests, its sublethal effects on non-target species, including parasitoids, have been documented and may account for the reduced reproductive potential observed in this study63. Sublethal exposures of these insecticides have been shown to impair key physiological processes such as oviposition, mobility, and longevity in parasitoids including T. chilonis, ultimately reducing their population growth potential64,65. The differences in R₀ and r have practical implications for the field efficacy of T. chilonis in pest suppression. A higher R₀implies greater reproductive output and a faster population buildup, enhancing the parasitoid’s ability to suppress pest populations over successive generations59. If insecticides reduce R₀, the reproductive output of T. chilonismay decline, limiting its ability to establish and sustain populations in pest-infested fields66. Therefore, reduced R₀ and r values due to Imidacloprid and Chlorantraniliprole exposure may compromise the establishment and sustainability of T. chilonis populations in treated fields, potentially undermining its effectiveness as a biological control agent. The finite rate of increase (λ), which represents the per capita multiplication rate of a population over a specific time, is an important parameter for assessing population growth potential under different environmental and treatment conditions. In this study, λ was significantly influenced by insecticide treatments. The highest λ values were recorded in the control (1.41 ± 9.45), Bifenthrin (1.39 ± 1.03), and Novaluron (1.38 ± 1.09) treatments, indicating their minimal negative impact on the population growth of T. chilonis. The high λvalues observed with Bifenthrin and Novaluron align with their relatively selective modes of action13,39. The control treatment showed the highest λ, representing the natural growth potential of T. chilonis populations in the absence of any external stressors. These results suggest that Bifenthrin and Novaluron are compatible with the biological control activities of T. chilonis, as they allow for near-optimal population growth rates, comparable to untreated conditions. In contrast, insecticides such as Imidacloprid, Chlorantraniliprole, and Emamectin Benzoate tend to negatively affect λ. This is likely due to their broader physiological impacts, which can include reduced fecundity, impaired mobility, and shorter lifespans in parasitoids65,67. Such reductions in λ could hinder the ability of T. chilonis to build up sufficient population densities to effectively suppress pest populations in field conditions. Mean Generation Time (T) represents the average time required for a population to complete one generation. It plays a crucial role in determining how quickly a biological control agent, such as T. chilonis, can respond to pest outbreaks. Shorter Tsignifies faster generational turnover, allowing for a rapid buildup of populations to suppress pests68. Conversely, prolonged T, as influenced by certain insecticides, may hinder the timely establishment of parasitoid populations in the field, thus reducing their overall effectiveness in managing pest populations. In the current study, the application of Novaluron resulted in significantly lower T values compared to control and other insecticide treatments. On the other hand, treatments with insecticides such as Imidacloprid and Chlorantraniliprole are associated with prolonged T. These insecticides have been reported to exert sublethal effects that impair various physiological and behavioral traits, such as development time, reproduction, and mobility69. Doubling Time (DT), another critical demographic parameter, reflects the time required for a population to double in size. Shorter DT indicates faster population growth, enabling T. chilonis to exert substantial pest suppression pressure. In contrast, longer DT, often observed following exposure to certain insecticides, suggests slower population expansion, potentially resulting in inadequate pest control and increased risks of pest resurgence14. These results are also aligned with the work of Carvalho et al.69, who also obtained similar results, noting that Imidacloprid negatively affected the parasitization capacity of T. pretiosum females of the F1 generation when applied in pre-adult stages, while the insecticides Novaluron and Triflumuron, when applied during the immature stages to T. pretiosum, were harmless to its F1 and F2 generations. The practical implications of these parameters are significant. For instance, a reduction in R₀, r, or λ, or an increase in T or DT due to synthetic insecticides, would weaken the ability of T. chilonis to suppress pest populations effectively. This underscores the importance of selecting insecticides that are compatible with biological control agents to ensure the sustainability of integrated pest management (IPM) programs. The effect of different insecticides on survival rate (sxj) showed that the maximum survival rate of the male and female adults of T. chilonis was recorded in Novaluron while lowest with Imidacloprid. These results agree with the results of Hewa-Kapuge et al.70 who reported > 64% mortality in residue assays when treated with Imidacloprid, Emamectin Benzoate, and Tau-fluvalinate after 1 h application. The effect of different insecticides on age specific life-expectancy (exj) of T. chilonis showed that the Imidacloprid resulted in lower exj values of T. chilonis adults. Ko et al.71also tested different insecticides on the life stages of Trichogramma and reported that thiamethoxam applied at larval stage and Imidacloprid and Buprofezin at prepupal stage resulted in > 30% reduction in emergence rate as compared with the control. The effect of the selected insecticides on T. chilonis reproductive value showed that the insecticides Novaluron and Bifenthrin were found relatively safer with maximum reproductive of T. chilonis. The insecticide Emamectin Benzoate was found to be moderately toxic to the T. chilonis while the Imidacloprid and Chlorantraniliprole were found to be highly toxic to T. chilonis with minimum reproductive values of T. chilonis. Similar results were also published by Nozad-Bonab et al.72 who reported Abamectin and Indoxacarb as slightly and moderately toxic against T. brassicae. Our results showed that the highest percentage parasitism was noted in control, Bifenthrin and Novaluron treatments. The insecticides Imidacloprid and Chlorantraniliprole were found to be more toxic and resulted in minimum % parasitism (63.5%, 71.00%) respectively. Similarly, the highest number of females emerged in control, followed by Bifenthrin and Novaluron, and the lowest in Chlorantraniliprole and Imidacloprid. Emamectin Benzoate was found slightly toxic with mean numbers of female (87) and male (65). These findings are aligned with the work of Liu and Zhang73, who reported reduced adult emergence and parasitization rate of T. chilonis. Visnupriya and Muthukrishan73 also noted adverse effect of insecticides and neem oil, reporting only 60% parasitism in treated host eggs. The study concluded that the insecticides Bifenthrin and Novaluron with little or no harmful effects on the parasitoid can be used in conjunction with T. chilonis in IPM programs. Future research should prioritize field-based trials to validate the laboratory findings under natural conditions and assess the real-world efficacy of insecticides on T. chilonis and pest populations. Additionally, testing the compatibility of these insecticides with other biocontrol agents, such as predators and alternative parasitoids, could broaden their application in integrated pest management (IPM). Exploring alternative formulations, such as encapsulated or slow-release forms, and application methods, like spot spraying, may reduce the negative effects on T. chilonis. Long-term studies on the population dynamics of T. chilonis across generations would provide insights into recovery potential or adaptation to insecticides. Lastly, research should investigate combining selective insecticides with other pest control methods to enhance sustainability and effectiveness in IPM programs.